Holocene sedimentary facies in the incised valley of Ma River Delta, Vietnam

Holocene sediment facies in the incised valley of the Ma River Delta were clarified by using analysis of LKTH6 core (30 m depth) such as sedimentary structure analysis, grain-sized, micro-paleontological (foraminifera, spore and pollen, and diatom), clay minerals characteristics, and Radiocarbon dating (14C). Ten sedimentary facies were identified, including (1) flood plain silty clay facies, (2) Salt marsh clayey silt facies, (3) Tidal flat sandy silty clay facies, (4) Tidal creek and tidal branch silty clayey sand facies, (5) Bay silty clay facies, (6) Prodelta silty clay facies, (7) Delta front silty sand facies, (8) Mouth bar sand facies, (9) Point bar silty sand faces, and (10) Alluvial plain silty clay facies. The sea level change after the last glacial was recorded by sediment facies and radiocarbon dating (14C). It showed that the Thanh Hoa coastal area drowned around 9500 yr. B.P. by transgression. At 9200 yr. B.P. initial marine flooding surface, tidal flats were formed in the coastal estuary area. During the period of 9200 -8300 yr. B.P., due to rapid sea level rise, the study area became an estuarine around 7600 yr. B.P., the sea level rose slowly, leading to the sea level rise rate being smaller than the sedimentary accumulation rate, and the delta was formed.